JP2007272031A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of restraining excessive temperature rise in an area through which recording material having narrower width than the heating area width of a heating body does not pass. <P>SOLUTION: The image forming apparatus performs control to reduce the number of output sheets of recording material per unit time on the basis of decision threshold temperature Ta corresponding to the length in the conveying direction of the recording material P detected by a length detection means 49 in such a state that the recording material P is not detected by a recording material existence detection means 68. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that forms an image on a recording material.

  In image forming apparatuses such as electrophotographic copying machines, printers, and facsimile machines, an electrostatic latent image is formed on the outer peripheral surface (surface) of a drum-shaped electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) that is an image carrier. An image is formed, and the latent image is developed as a toner image by a developing device. The toner image (development image) on the surface of the photosensitive drum is transferred onto a recording material by a transfer device, and the toner image on the recording material is heated and fixed on the recording material surface by an image heating fixing device (fixing device).

  As the fixing device, a heating body that generates heat by energization, a heat-resistant film that slides with the heating body, a pressure member that presses the heating body across the film to form a nip portion and the film, Some have In this film heating type fixing device, a heating body is heated and adjusted to a predetermined temperature, and a recording material on which an unfixed toner image is formed and held is nipped and conveyed at the nip portion. The toner image is applied with heat from the heating member and pressure from the pressure member. As a result, the toner image is fixed on the recording material surface as a permanently fixed image.

  In the fixing device, a thin plate-like heating body having a low heat capacity such as a so-called ceramic heater can be used as the heating body, and a thin film having a low heat capacity can be used as the film. Therefore, it is possible to quickly raise the temperature of the nip portion to the set temperature (target temperature). For this reason, since power can be suppressed as much as possible without supplying power to the apparatus during standby, power saving and wait time reduction (quick start performance) can be realized (Patent Documents 1, 2, 3, and 4). reference).

  In the fixing device, when a recording material (for example, an envelope or a postcard) having a narrow width with respect to the heat generation area width in the longitudinal direction of the plate-like heating body is nipped and conveyed at the nip portion, an area through which the recording material passes (paper passing area) And the region that does not pass through (non-paper passing region), the amount of heat taken away from the heating body is greatly different. Therefore, when a narrow recording material is continuously nipped and conveyed at the nip portion, heat is not taken away by the recording material in an area where the recording material does not pass. Therefore, the temperature of the area gradually increases as the number of conveyed recording materials increases. The temperature rises to exceed the set temperature, and a so-called non-sheet passing portion temperature rise phenomenon occurs. Excessive temperature rise of the non-sheet passing portion significantly exceeding the set temperature may damage constituent members such as a film and a pressure member, thereby reducing the device life (durability life).

Therefore, an attempt has been made to reduce the interval between recording materials that are continuously conveyed, so-called throughput (the number of recording materials conveyed (output) per unit time) to a point where there is no problem even under the worst conditions. In Patent Document 5, a temperature detection unit such as a thermistor provided in a non-sheet passing region detects temperature rise of the non-sheet passing portion, and the throughput is changed according to the temperature state, the conveyance speed is lowered, or the heating body is changed. The control of temporarily stopping the power supply is proposed.
JP-A-63-313182 Japanese Patent Laid-Open No. 2-157878 JP-A-4-44075 JP-A-4-204980 JP-A-2005-284021

  The present invention is a further development of the prior art. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an image forming apparatus capable of suppressing an excessive temperature rise in an area where a recording material narrower than a heating area width of a heating body does not pass.

A typical configuration of an image forming apparatus according to the present invention is an image forming apparatus that forms an image on a recording material, and includes an elongated heating body that heats a recording material that generates heat by energization and carries the image, A first temperature detecting means for detecting a temperature of a region through which a recording material having a narrow width with respect to a heat generation region width in a longitudinal direction; and a first temperature detecting unit for detecting a temperature of a region through which the recording material does not pass with respect to the heat generation region width. And controlling the energization to the heating body so as to maintain the detected temperature of the two temperature detecting means and the first temperature detecting means at a set temperature, and per unit time based on the detected temperature of the second temperature detecting means. An image forming apparatus having control means for performing control to reduce the number of output recording materials,
A length detection means for detecting the length of the recording material in the transport direction;
Recording material presence / absence detecting means for detecting the presence / absence of the recording material on the side opposite to the second temperature detecting means with respect to a recording material conveyance reference for conveying the recording material to the heating body;
Have
The control means is a threshold temperature for performing control to reduce the number of output recording materials per unit time based on the detected temperature of the second temperature detecting means for the recording materials having different lengths in the conveyance direction of the recording material. And the threshold temperature is lower when the recording material is not detected by the recording material presence / absence detection means and the length of the recording material detected by the length detection means is longer than a reference length. The image forming apparatus is characterized by being set to be higher.

A typical configuration of the image forming apparatus according to the present invention is an image forming apparatus that forms an image on a recording material, the elongated heating body that heats the recording material that generates heat by energization and carries the image, and the heating A first temperature detecting means for detecting a temperature of a region through which a recording material narrow in the longitudinal direction of the body passes; and a region in which the recording material narrow in width does not pass through the heat generating region width. A second temperature detecting means for detecting the temperature, and controlling the energization to the heating body so as to maintain the detected temperature of the first temperature detecting means at a set temperature, and based on the detected temperature of the second temperature detecting means And an image forming apparatus having control means for controlling to reduce the number of recording material outputs per unit time,
A length detection means for detecting a length in the conveyance direction of the recording material conveyed to the heating body;
Recording material presence / absence detecting means for detecting the presence / absence of the recording material on the side opposite to the second temperature detecting means with respect to a recording material conveyance reference for conveying the recording material to the heating body;
Have
The control means is a threshold time for performing control to reduce the number of output recording materials per unit time based on the detected temperature of the second temperature detecting means for the recording materials having different lengths in the conveyance direction of the recording material. And the threshold time is shorter when the recording material is not detected by the recording material presence / absence detection means and the length of the recording material detected by the length detection means is longer than a reference length. The image forming apparatus is characterized by being set to be shorter.

  According to the present invention, it is possible to provide an image forming apparatus capable of suppressing an excessive temperature rise in an area where a recording material narrower than a heating area width of a heating body does not pass.

  Hereinafter, the present invention will be described in detail with reference to the drawings.

(1) Example of Image Forming Apparatus FIG. 1 is a structural model diagram of an example of an image forming apparatus according to the present invention.

  The image forming apparatus according to the present exemplary embodiment is a full-color image forming apparatus that forms four color images of yellow, cyan, magenta, and black on a recording material using an electrophotographic method. The process speed of this apparatus is 180 mm / second, and the number of printed sheets per minute is 30 sheets of US letter size paper. Here, the process speed is a speed at which an image is formed on a recording material.

  The image forming apparatus includes an image forming mechanism unit 102 that forms an image on a recording material P, a recording material conveyance mechanism unit 103 as a recording material conveyance unit, and an image heating unit. And an image heating and fixing device 104 as an apparatus. The recording material conveyance mechanism unit 103 includes a feeding cassette 10 as a first recording material supply unit at a lower portion of the apparatus main body 101, and is manually inserted as a second recording material supply unit at a predetermined side surface of the apparatus main body 101. A tray 41 is provided.

  In the image forming mechanism 102, Y, C, M, and K are four process cartridges that respectively form yellow, cyan, magenta, and black color toner images, and are arranged in the apparatus main body 100 in that order from the bottom to the top. It is. Each of the cartridges Y, C, M, and K includes a photosensitive drum 1 as an image carrier, a charging roller 2 as a charging unit, a developing device 3 as a developing unit, a cleaning container 4 as a cleaning unit, and the like. The cartridge frame is provided. The developing device 3 of the yellow cartridge Y is filled with yellow toner. The developing device 3 of the cyan cartridge C is filled with cyan toner. The developing device 3 of the magenta cartridge M is filled with magenta toner. The developing device means 3 of the black cartridge K is filled with black toner.

  An optical system 5 for forming an electrostatic latent image by exposing the photosensitive drum 1 is provided in the apparatus main body 100 corresponding to the four color cartridges Y, C, M, and K. As the optical system 5, a laser scanning exposure optical system is used.

  The photosensitive drums 1 of the cartridges Y, C, M, and K are rotated at a predetermined peripheral speed (process speed) in the arrow direction. Then, the outer peripheral surface (front surface) of the photosensitive drum 1 is uniformly charged to a predetermined potential and polarity by the charging roller 2. Then, scanning exposure corresponding to image data is performed on the charged surface of the surface of the photosensitive drum 1 by the optical system 5. Thereby, an electrostatic latent image is formed on the surface of the photosensitive drum 1. A developing bias is applied to a developing roller provided in the developing device 3 from a bias power source (not shown). By the developing bias, the toner is transferred from the outer peripheral surface (surface) of the developing roller to the surface of the photosensitive drum 1 and attached to the latent image. As a result, the latent image on the photosensitive drum 1 of the cartridge Y is developed as a yellow toner image. Further, the latent image on the photosensitive drum 1 of the cartridge C is developed as a cyan toner image. Further, the latent image on the photosensitive drum 1 of the cartridge M is developed as a magenta toner image. Then, the latent image on the photosensitive drum 1 of the cartridge K is developed as a black toner image.

  The toner images on the photosensitive drums 1 are sequentially superimposed on the intermediate transfer member 6 that rotates at a substantially constant speed in synchronization with the rotation of the photosensitive drums 1 in order by the primary transfer unit 9 in order. Transcribed. An endless intermediate transfer belt as the intermediate transfer member 6 is suspended and stretched by three rollers, a driving roller 7, a secondary transfer roller facing roller 14, and a tension roller 8, which are rotatably held by the apparatus main body 101. And is rotated by the drive roller 7. A primary transfer bias having a polarity opposite to that of toner is applied to a primary transfer roller as the primary transfer unit 9 from a bias power source (not shown). The toner image is primarily transferred from the surface of the photosensitive drum 1 to the belt 6 by the transfer bias. As a result, four full-color toner images are synthesized and formed on the belt 6.

  Transfer residual toner remaining on the photosensitive drum 1 after the primary transfer from the photosensitive drum 1 to the belt 6 is scraped off and removed by a cleaning blade provided in the cleaning device 4. In this embodiment, a urethane blade is used as the cleaning blade.

  In the image forming apparatus according to the present exemplary embodiment, it is possible to perform single-color image formation (single-color mode). In this case, the latent image, development, and primary transfer processes are performed only on the target color toner image.

  On the other hand, in the recording material transport mechanism 103, the recording material P is sent out from either the feeding cassette 10 or the manual feed tray 41 to the image forming mechanism 102. In the cassette 10, recording materials P of the same size that can be used in the image forming apparatus are stacked and stored. The recording material P in the cassette 10 is sent to the registration roller 13 through the transport roller 12 one by one as the feed roller 11 rotates once. On the tray 41, a recording material P having an arbitrary size usable for the image forming apparatus is set by the user. The recording material P set on the tray 41 is sent to the registration roller 13 one by one when the feeding roller 42 rotates once. The registration roller 13 conveys the recording material P at a predetermined timing to a secondary transfer nip portion that is a pressure contact portion between the belt 6 portion wound around the secondary transfer counter roller 14 and the secondary transfer roller 15.

  In the image forming mechanism unit 102, the primary transfer composite toner image formed on the belt 6 is collectively transferred onto the recording material P at the secondary transfer nip portion. A bias having a polarity opposite to that of the toner is applied to the secondary transfer roller 15 from a bias power source (not shown). As a result, the primary transfer composite toner image on the belt 6 is electrostatically transferred onto the recording material P.

  The secondary transfer residual toner remaining on the belt 6 after the secondary transfer is scraped off and removed by a cleaning blade provided in a belt cleaning device 16 as an intermediate transfer belt cleaning unit. In this embodiment, a urethane blade is used as the cleaning blade in the same manner as the cleaning blade of the photosensitive drum 1.

  The recording material P that has passed through the secondary transfer nip is separated from the belt 6 by the curvature and conveyed to the fixing device 104. The fixing device 104 pressurizes, heats and melts the toner image on the recording material P to fix it as a permanently fixed image on the recording material surface. The recording material P that has undergone the fixing process is discharged as a full-color print onto the discharge tray 32 through the discharge path 31 of the recording material transport mechanism 103.

(2) Fixing device 104
FIG. 2 is a schematic cross-sectional side view of an example of the fixing device 104. The fixing device 104 according to the present exemplary embodiment is a fixing rotating member heating method and a pressure rotating member driving method (tensionless type) fixing device.

1) Overall Configuration of Fixing Device 104 Reference numeral 20 denotes a fixing belt as a fixing rotating body, which is a cylindrical (endless belt-like) member elongated in the width direction perpendicular to the conveyance direction of the recording material P. The belt 20 has a base layer of a SUS belt formed by drawing a SUS base tube into a seamless belt shape having a thickness of 50 μm. A silicone rubber layer having a thickness of 250 μm is formed as an elastic layer on the SUS belt by a ring coating method. Further, a PFA resin tube having a thickness of 30 μm is coated on the rubber layer as a release layer. Thereby, it is possible to prevent the offset phenomenon that occurs when the toner once adheres to the surface of the belt 20 and the toner moves to the recording material P again. The belt 20 is loosely fitted around a heater holder 17 as a holding member.

  The heater holder 17 is a member having heat resistance and rigidity having a substantially semicircular arc cross-sectional shape elongated in the width direction perpendicular to the conveyance direction of the recording material P. The holder 17 is made of a liquid crystal polymer resin having high heat resistance. The holder 17 is arranged inside the belt 20 to guide the belt 20 and to hold a heater 18 as a heating body (heat source). Xenite 7755 (trade name) manufactured by DuPont was used as the liquid crystal polymer. The maximum usable temperature of Zenite 7755 is about 270 ° C.

  The elastic pressure roller 22 as a pressure rotator is a member that is elongated in the width direction orthogonal to the conveying direction of the recording material P, and has a thickness of about 3 mm by injection molding as an elastic layer 22b around a stainless steel core 22a. A silicone rubber layer is formed. A PFA resin tube having a thickness of about 40 μm is coated on the elastic layer 22b as a release layer 22c. The pressure roller 22 is arranged such that both end portions of the cored bar 22a are rotatably supported by bearings between a side plate (not shown) on the back side and a front side of the apparatus frame 24. On the upper side of the pressure roller 22, a heating assembly including the heater 18, the holder 17, the belt 20 and the like is arranged in parallel with the pressure roller 22 with the heater 18 facing downward. Then, both ends of the holder 17 are urged in the axial direction of the pressure roller 22 by a force of 98 N (10 kgf) on one side and a total pressure of 196 N (20 kgf) by a pressure mechanism (not shown), so that the heater 18 is attached to the belt 20. The pressure is applied to the elastic layer 22 b of the pressure roller 22. By this pressurization, the elastic layer 22b is elastically deformed to form a nip portion (fixing nip portion) N having a predetermined width necessary for heat fixing.

  65 is a main thermistor as a first temperature detecting means. The main thermistor 65 has a thermistor element 65b at the tip of a stainless steel arm 65a fixedly supported by the holder 17, and the thermistor element 65b is elastically brought into contact with the inner surface of the belt 20 by the arm 65a. Therefore, even if the movement of the inner surface of the belt 20 becomes unstable during the rotation of the belt 20, the thermistor element 65b can always be in contact with the inner surface of the belt 20.

  Reference numeral 23 denotes an entrance guide assembled to the apparatus frame 24. The entrance guide 23 plays a role of accurately guiding the recording material P conveyed from the secondary transfer nip to the nip portion N. The entrance guide 23 is made of polyphenylene sulfide (PPS) resin. Reference numeral 29 denotes a fixing paper discharge roller assembled to the apparatus frame 24.

  Reference numeral 19 denotes a thermo switch as temperature detecting means for safety measures. The thermo switch 67 is held by the heater 18 via the spacer 25. And it is urged | biased by the heater 18 side with the spring 26 which is an urging | biasing member. The thermo switch 67 is connected in series to a power supply line (AC line) (not shown) that supplies power to the heater 18, and cuts off the power supply to the heater 18 when a temperature equal to or higher than a predetermined temperature is detected.

2) Structure of the heater 18 FIG. 3 is a structural model diagram of an example of the heater 18, wherein (a) is a partially cutaway surface model diagram, (b) is a back surface model diagram, and (c) is an enlarged cross-sectional model diagram. is there.

  The heater 18 includes an aluminum nitride substrate a that is elongated in the width direction perpendicular to the conveyance direction of the recording material P. A linear or belt-like resistance heating element b is formed on the surface side of the substrate a by screen printing along the longitudinal direction. The heating element b is a conductive paste containing a silver-palladium (Ag / Pd) alloy that generates heat when an electric current flows, and has a thickness of about 10 μm and a width of about 1 to 5 mm. The resistance of the heating element a is adjusted so that the resistance value becomes 12Ω.

  As a power supply pattern for the heating element b, the first and second electrode portions c and d and the extended electric circuit portions e and f are formed by patterning silver paste screen printing or the like on one end in the longitudinal direction on the surface side of the substrate a. .

  A glass coat g as a protective layer is formed on the heating element b and the extension circuit portion e · f in order to ensure protection and insulation. The thickness of the glass coat g is about 10 μm.

  A sliding layer h coated with a polyimide resin with a thickness of about 6 μm is provided on the surface of the substrate a on the recording material P side, that is, the back surface side, in order to ensure slidability with the inner surface of the belt 20.

  The heater 18 is fixed to and supported by the holder 17 with the surface side of the substrate a facing upward.

  A power feeding connector 27 is attached to the electrode portions c and d of the heater 18. Power is supplied to the electrode portions cd from the heater drive circuit portion 28 as heater drive means via the connector 27.

3) Heat-fixing operation of the fixing device 104 The pressure roller 22 is rotated at a predetermined peripheral speed (process speed) by a rotation driving mechanism M as a rotation driving unit. A rotational force acts on the belt 20 by the pressure friction force in the nip portion N between the surface of the pressure roller 22 and the surface of the belt 20 due to the rotation of the pressure roller 22. Due to this rotational force, the belt 20 is driven to rotate around the outside of the holder 17 in the direction of the arrow while the inner surface of the belt 20 is in close contact with the surface of the sliding layer h of the heater 18 and slides. Grease is applied to the inner surface of the belt 20. Thereby, the slidability between the holder 17 and the inner surface of the belt 20 is ensured.

  In the rotating state of the pressure roller 22 and the belt 20, the heater element b is energized from the heater drive circuit section 28 through the electrode sections c and d and the extension circuit sections e and f of the heater 18. As a result, the heating element b generates heat and the heater 18 quickly rises in temperature. Accordingly, the width of the heating element b formed in the heater 18 along the longitudinal direction of the substrate a becomes the heating area width. In the heater drive circuit unit 28, energization to the heater 18 is controlled by a DC controller (CPU) 21 as control means. That is, the controller 21 controls the heater drive circuit unit 28 so that the detected temperature of the main thermistor 65 becomes a predetermined set temperature (target temperature) T (= 195 ° C.).

  The recording material P carrying the unfixed toner image t between the belt 20 and the pressure roller 22 in the nip portion N along the entrance guide 23 in a state where the heater 18 is heated and adjusted to the set temperature. Guided and introduced. The recording material P is nipped and conveyed in the nip portion N together with the belt 20 with the toner image carrying surface side in close contact with the outer surface of the belt 20 in the nip portion N. In this nipping and conveying process, the heat of the heater 18 is applied to the recording material P via the belt 20, and the unfixed toner image t on the recording material P is heated and pressurized on the recording material P to be melted and fixed. The recording material P that has exited the nip N is separated from the surface of the belt 20 by the curvature, and is discharged by the fixing discharge roller 29.

(3) Configuration of tray 41 and recording material presence / absence sensors 48, 49, 68
FIG. 4 is a transmission plane model diagram of the image forming apparatus. The recording material P conveyance standard (sheet passing standard) in the image forming apparatus is a central conveyance standard for conveying the recording material P based on the center between the end faces in the width direction orthogonal to the recording material P conveying direction (hereinafter referred to as paper passing). A) (referred to as position reference).

  In the tray 41, width regulation guides 43L and 43R as a pair of left and right width regulation members arranged in the width direction orthogonal to the conveyance direction of the recording material P are connected by a synchronous movement mechanism (not shown), It can move in a symmetrical manner with respect to the position reference A. Thus, the interval between the guides 43L and 43R can be adjusted to be wide or narrow with the sheet position reference A as the center. That is, with the guides 43L and 43R being expanded in the width direction, the recording material P is placed on the tray 41 between the guides 43L and 43R, and the guides 43L and 43R are moved in accordance with the width of the recording material P. . As a result, the left and right end surfaces of the recording material P are regulated by the left and right inner surfaces of the guides 43L and 43R, the recording material P is on the tray 41 and the width center coincides with the sheet passing position reference A, and the recording material P is in that state. Set to The feeding roller 42 rotatably supported on the tray 41 is rotated by the rotation driving mechanism M, and conveys the recording material P set on the tray 41 to the registration roller 13 (FIG. 1).

  In the width direction of the tray 41, a region (L2 + L2) symmetrical with respect to the sheet passing position reference A is the maximum width dimension of the recording material P that guarantees manual feeding, and has the same dimension as the heating element b width of the heater 18. . A region (L1 + L1) symmetrical with respect to the sheet passing position reference A is the minimum width dimension of the recording material P that guarantees manual feeding. In this embodiment, the maximum width dimension (L2 + L2) is the LTR size (216 mm), and the minimum width dimension (L1 + L1) is a business card size of 76.2 mm × 127 mm.

  The main thermistor 65 is disposed at a position 30 mm away from the sheet passing position reference A within the region of the minimum width dimension (L1 + L1). Therefore, by this main thermistor 65, the area of the inner surface of the belt 20 corresponding to the area (sheet passing area) through which the recording material P having a minimum width (L1 + L1) with respect to the width of the heating element b of the heater 18 passes. Temperature can be detected. Therefore, when the narrow recording material P having the minimum width dimension (L1 + L1) is introduced into the nip portion N, the controller 21 controls the temperature of the heater 18 to the set temperature based on the temperature detected by the main thermistor 65.

  Reference numeral 66 denotes a sub-thermistor as second temperature detecting means. The sub-thermistor 66 has a distance L4 (= 95 mm) from the sheet passing position reference A within the difference area (2L2-2L1 / 2) between the minimum width dimension (L1 + L1) and the maximum width dimension (L2 + L2) on the substrate a surface side of the heater 18. ) It is arranged at a distant position. The sub-thermistor 66 can detect the temperature rise at the end of the heater 18 for the recording material P having a B5 size width (182 mm) or less. Therefore, by this sub-thermistor 66, a region on the surface side of the substrate a corresponding to a region (non-sheet passing portion region) where the recording material P having a B5 size width (182 mm) or less with respect to the heating element b width of the heater 18 does not pass. Temperature can be detected. Therefore, when the recording material P of B5 size width or less is continuously introduced into the nip portion N, the controller 21 determines the throughput of the recording material P based on the detected temperature of the sub-thermistor 66 (per unit time of the recording material). Control to lower the (transport (output) number of sheets). This throughput down control will be described in detail later.

  The thermo switch 67 is disposed at a position 25 mm away from the sheet passing position reference A in the area of the minimum width dimension (L1 + L1) on the substrate a surface side of the heater 18. The thermo switch 67 is disposed on the opposite side of the main thermistor 65 with the sheet passing position reference A therebetween.

  Reference numeral 48 denotes a recording material sensor as recording material detection means, which is disposed in the region of the minimum width dimension (L1 + L1) between the guides 43L and 43R of the tray 41 and the feeding roller. Therefore, the recording material sensor 48 can detect the presence or absence of the recording material P having a minimum width dimension (L1 + L1) or more.

  Reference numeral 49 denotes a top sensor 49 as a length detecting means, which is disposed in the region of the minimum width dimension (L1 + L1) between the registration roller 13 and the secondary transfer roller 15 (FIG. 1). Therefore, the top sensor 49 can detect the length in the transport direction for the recording material P having the minimum width dimension (L1 + L1) or more.

  Reference numeral 68 denotes a recording material shift sensor as a recording material presence / absence detecting means, and a difference area (2L2) between the minimum width dimension (L1 + L1) and the maximum width dimension (L2 + L2) between the conveying roller 12 and the registration roller 13 (FIG. 1). -2L1 / 2). The misalignment sensor 68 is arranged on the opposite side of the sub-thermistor 66 with the sheet passing position reference A in between, and is located at a distance L5 (= 95 mm) from the sheet passing position reference A. Therefore, when the recording material P having an A4 size width (210 mm) is transported from the tray 41 on the basis of the central transport reference, the recording material P passes the misalignment sensor 68. Can be detected. However, when the recording material P having a B5 size width (183 mm) or less is conveyed from the tray 41 on the basis of the central conveyance reference, the recording material P does not pass the misalignment sensor 68. Cannot be detected.

(4) Conveying pattern of recording material P fed from tray 41 When recording material P is fed from tray 41 and image formation (printing) is performed, recording material P is fed from tray 41 to image forming mechanism 102. There are two ways to do this. One is a form within the specification in which the recording material P is conveyed by the feeding roller 42 in a state where the guides 43L and 43R are adjusted to the width of the recording material P. The other is a form out of the specification in which the guides 43L and 43R are extended to the maximum and, for example, an envelope having a width of 110 mm as the recording material P is conveyed by the feeding roller 42 in a state of being brought close to the right guide 43R.

  Further, the conveyance patterns for feeding the recording material P having different sizes from the tray 41 to the image forming mechanism unit 102 can be classified into the following four patterns including those within the specification and those outside the specification.

Pattern I: Large size recording material P within specifications is set on tray 41 (FIG. 5)
Pattern II: A small-sized recording material P within the specification is set on the tray 41 (FIG. 4).
Pattern III: A recording material P of a small size that is out of specification is set on the tray 41 (FIG. 6: side-aligned to the side-alignment sensor 68 side)
Pattern IV: A small-size recording material P outside the specification is set on the tray 41 (FIG. 7: shifted to the sub-thermistor 19 side)
Here, the large-sized recording material P is a recording material having a width that does not cause a temperature increase in the non-sheet passing portion at the nip portion N of the fixing device 104. The large-size recording material P is also a wide recording material that passes through the offset sensor 68. The small size recording material P is a recording material having a width in which the temperature rise of the non-sheet passing portion occurs in the nip portion N of the fixing device 104. The small-size recording material P is also a narrow recording material that does not pass the offset sensor 68.

  When a large-sized recording material P is fed from the tray 41 in the pattern I, the recording material P can be detected by the shift sensor 68, and therefore the controller 21 determines that the recording material P is on the shift sensor 68 side. Since the sub-thermistor 66 is in the sheet passing area of the recording material P, it does not detect excessive temperature rise. Therefore, the controller 21 performs control to rotate the feeding roller 42 so that the recording material P is fed at a normal throughput corresponding to the process speed described above.

  When a small-sized recording material P is fed from the tray 41 in the pattern II, the recording material P cannot be detected by the offset sensor 68, and therefore the controller 21 determines that there is no recording material P on the offset sensor 68 side. . Since the sub-thermistor 66 is in the non-sheet passing portion region of the recording material P, it detects an excessive temperature rise (non-sheet passing portion temperature rise).

  When a small-sized recording material P is fed from the tray 41 in the pattern III, the recording material P can be detected by the shift sensor 68, and therefore the controller 21 determines that the recording material P is on the shift sensor 68 side. Since the sub-thermistor 66 is in the non-sheet passing portion region of the recording material P, it detects an excessive temperature rise (non-sheet passing portion temperature rise). Therefore, the controller 21 performs small size throughput down control according to the temperature detected by the sub-thermistor 66.

  When a small size recording material P is fed from the tray 41 in the pattern IV, the recording material P cannot be detected by the shift sensor 68, and therefore the controller 21 determines that there is no recording material P on the shift sensor 68 side. . Since the sub-thermistor 66 is in the sheet passing area of the recording material P, it does not detect excessive temperature rise. In this case, the controller 21 cannot perform small size throughput down control based on the temperature detected by the sub-thermistor 66. Therefore, the controller 21 performs a justification throughput down control which will be described later.

  Here, the conveyance mode of the recording material P shown in the pattern III and the pattern IV is referred to as a side-by-side sheet.

  FIG. 8 is a determination flowchart of the small size throughput down control and the offset throughput down control by the controller 21.

  In the controller 21, it is determined whether to execute the small size throughput down control or the side shift paper throughput reduction control based on whether or not the recording material P is detected by the registration sensor 68. When the recording material P is detected, small size throughput down control is executed. When the recording material P is not detected, the offset throughput reduction control is executed.

(5) Small Size Throughput Down Control and Misaligned Throughput Down Control 1) Small Size Throughput Down Control FIG. 9 is a flowchart of small size throughput down control.

  The small size throughput down control refers to a case where the sub thermistor temperature Ts detected by the sub thermistor 66 during the continuous feeding of the recording material P exceeds the temperature Th in the non-sheet passing portion temperature rising state. This is control for reducing the throughput of the recording material P. In this embodiment, when the sub-thermistor temperature Ts is detected as Th = 250 ° C., the throughput is reduced by controlling the rotation of the feeding roller 42 so as to widen the feeding pick interval of the recording material P.

  Specifically, when 250 ° C. is detected as described below, the throughput is gradually reduced from the normal throughput F0. Reduce from F0 = 30 ppm to F1 = 15 ppm. Further, when the temperature exceeds 250 ° C. during continuous paper feeding, the pressure is reduced from F1 = 15 ppm to F2 = 7.5 ppm. Furthermore, when it exceeds 250 degreeC, it will fall from F2 = 7.5ppm to F3 = 3ppm. If it is lowered to 3 ppm, it has been confirmed that the recording device P of any size usable in the image forming apparatus does not damage the fixing device 104 due to the temperature rise of the non-sheet passing portion even if the sheet is continuously fed.

  As described above, when the detected temperature of the sub-thermistor 66 exceeds 250 ° C., the throughput is reduced, thereby suppressing the temperature rise of the non-sheet passing portion.

2) Misalignment Throughput Down Control FIG. 10 is a flowchart of misalignment throughput down control.

  When the recording material P does not pass through the misalignment sensor 68, the misalignment throughput decrease determination threshold temperature Ta is set according to the length of the recording material P in the transport direction detected by the top sensor 49. When the sub-thermistor temperature Ts has not exceeded the threshold temperature Ta once at t seconds after the recording material P reaches the nip portion N (YES), it is determined that the sheet is in a justified sheet passing state shown in the pattern IV. If it is determined that the sheet is in a one-sided sheet passing state, the throughput is reduced to F3 = 3 ppm by performing control to rotate the feeding roller 42 so as to widen the feeding pick interval of the recording material P. In the case of one-sided sheet feeding, it is impossible to monitor the degree of non-sheet passing portion temperature rise by the sub-thermistor 66. Therefore, even if the recording material P is continuously fed, the non-sheet passing portion temperature rise causes the fixing device 104 to rise. The throughput is reduced to F3 that does not cause damage.

(6) Judgment throughput reduction judgment threshold temperature Ta
In order to execute the shift-down throughput control in the pattern IV, it is necessary to distinguish between the pattern II and the pattern IV in which the recording material P cannot be detected by the shift sensor 68. In the present embodiment, the controller 21 takes in the detected temperature of the sub-thermistor 66 and distinguishes the pattern II and the pattern IV depending on whether or not a predetermined temperature is reached after a certain time. In consideration of the temperature rise of the non-sheet passing portion, it is necessary to determine whether the pattern II or the pattern IV is within 15 seconds after the recording material P reaches the nip portion N. Depending on the length of the recording material P in the conveyance direction, the temperature detected by the sub-thermistor 66 in the non-sheet-passing area is different. In the recording material P, when the length in the transport direction is shorter than a predetermined reference length, the passing time through the nip portion N is shorter than when the length is longer than the predetermined reference length. That is, when the length of the recording material P in the conveyance direction is shorter than the reference length, the time during which power is supplied to the heater 18 is shorter than when the recording material P is longer than the reference length. For this reason, the shorter the length of the recording material P in the conveyance direction, the lower the non-sheet passing portion temperature rise per recording material P.

  FIG. 11 shows the relationship between the conveyance direction length of the recording material P and the temperature arrival time of the sub-thermistor 66 when the recording material P is passed through the nip portion N based on the central conveyance reference. It can be seen that when the length of the recording material P in the conveyance direction is short, the time for reaching the sub-thermistor temperature in the non-sheet passing portion region is longer than when the recording material P is long. Based on the result of FIG. 11, the judgment threshold temperature Ta for reducing the offset throughput may be determined. Further, the controller 21 changes the judgment threshold temperature Ta for shifting to a one-sided throughput reduction according to the length of the recording material P in the transport direction detected by the top sensor 49.

  FIG. 12 shows an example of the relationship between the conveyance direction length of the recording material P and the determination threshold temperature Ta. Three determination threshold temperatures Ta are set according to the length of the recording material P in the conveyance direction. Here, the reference length in the conveyance direction of the recording material P of the present embodiment is set to three of 127 mm, 170 mm, and 220 mm.

  In the case of the side-by-sheet passing state as in pattern II, the detection temperature of the sub-thermistor 66 in the non-sheet passing portion region of the recording material P reaches the judgment threshold temperature Ta shown in FIG. The controller 21 executes small size throughput down control. In the case of the sheet passing state as in pattern IV, the detection temperature of the sub-thermistor 66 in the sheet passing area of the recording material P does not reach the judgment threshold temperature Ta shown in FIG. 11 within 15 seconds. , The controller 21 executes the offset throughput down control.

  That is, the controller 21 has a plurality of determination threshold temperatures Ta for performing the shift-down throughput control based on the detected temperature of the sub-thermistor 66 for the recording materials P having different lengths in the transport direction. The determination threshold temperature Ta is set to be higher when the recording material P is not detected by the shift sensor 68 and the length of the recording material P detected by the top sensor 49 is longer than the reference length, when it is shorter. is there.

  According to this embodiment, the recording material P is not detected by the shift sensor 68 and the recording material P is detected based on the determination threshold temperature Ta corresponding to the length in the transport direction of the recording material P detected by the top sensor 49. On the other hand, small-size throughput down control or justified throughput down control is performed. For this reason, it is possible to suppress an excessive temperature rise in a region where the recording material P narrower than the width of the heating element b of the heater 18 does not pass, and the durability life of the fixing device 104 can be extended. In addition, it is possible to suppress unnecessary throughput reduction at the time of sheet feeding.

  Another example of the image forming apparatus according to the present invention will be described.

  In the present embodiment, the same members and portions as those in the image forming apparatus of the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

  In the image forming apparatus according to the first exemplary embodiment, the length of the recording material P in the conveyance direction is detected in order to distinguish the state of the pattern II from the state in which the recording material P is not detected by the shift sensor 68 and the state of the pattern IV. Accordingly, the determination threshold temperature Ta for shifting to a one-sided throughput is changed.

  The image forming apparatus according to the present exemplary embodiment is different from the image forming apparatus according to the first exemplary embodiment in a detection method for shifting to the justification throughput down control. The present embodiment is characterized in that the determination threshold temperature Ta is set to a fixed temperature of 250 ° C., and the determination threshold time ta for shifting to the justification throughput is changed according to the length of the recording material P in the conveyance direction. In the recording material P, when the length in the transport direction is shorter than the predetermined reference length, the determination threshold time ta is extended because the temperature rise of the non-sheet passing portion is reduced as compared with the case where the length is longer.

  FIG. 13 shows an example of the relationship between the length of the recording material P in the conveyance direction and the determination threshold time ta. Three determination threshold times ta are set according to the length of the recording material P in the conveyance direction. Here, the reference length in the conveyance direction of the recording material P of the present embodiment is set to three of 127 mm, 170 mm, and 220 mm. The determination threshold time ta is a time required for the detected temperature of the sub-thermistor to reach a certain threshold temperature (= 250 ° C.).

  In the case of a side-by-sheet passing state as in Pattern II, the detected temperature of the sub-thermistor 66 in the non-sheet passing portion region of the recording material P reaches a threshold temperature of 250 ° C. within the judgment threshold time ta shown in FIG. Therefore, the controller 21 executes small size throughput down control. In the case of a side-by-sheet passing state as in pattern IV, the detection temperature of the sub-thermistor 66 in the non-sheet-passing area of the recording material P reaches the threshold temperature 250 ° C. within the determination threshold time ta shown in FIG. Since it does not reach, the controller 21 executes the shift-down throughput control.

  That is, the controller 21 has a plurality of determination threshold times ta for performing the shift-down throughput control based on the temperature detected by the sub-thermistor 66 for the recording materials P having different lengths in the transport direction. This determination threshold time is set to be shorter when the recording material P is not detected by the shift sensor 68 and the length of the recording material P detected by the top sensor 49 is longer than the reference length. .

  According to this embodiment, the recording material P is not detected by the shift sensor 68 and the recording material P is detected based on the determination threshold time ta corresponding to the length in the transport direction of the recording material P detected by the top sensor 49. On the other hand, small-size throughput down control or justified throughput down control is performed. Therefore, the same effect as that of the first embodiment can be obtained. In the case of the recording material P having a short length in the transport direction, the determination threshold time ta becomes long, so that it is possible to extend the time during which the sheet can be passed with the normal throughput F0 even in the one-sided sheet passing state.

[Others]
1) In each embodiment, the top sensor 49 is used as the length detection means. However, the length detection means is not limited to this, and other means that can detect the length of the recording material P in the transport direction may be used instead. . Alternatively, a dedicated sensor may be used.

  2) In each embodiment, the conveyance speed of the recording material P is changed by widening the feeding pick interval of the recording material P by the feeding roller 42 to reduce the throughput. However, the throughput reduction is not limited to this, and the process speed is increased. It is also possible to reduce the throughput.

Configuration model diagram of an example of an image forming apparatus according to the present invention Cross-sectional side view of an example of a fixing device Structural model diagram of an example of a heater Transmission plane model diagram of the image forming apparatus and an explanatory diagram of a state in which a recording material of a small size within the specification is set on the tray Transmission plane model diagram of the image forming apparatus and explanatory diagram of a state in which a large-sized recording material is set on the tray within the specifications Transmission plane model diagram of the image forming apparatus, and explanatory diagram of a state in which a small size recording material is set on the tray out of specification Transmission plane model diagram of the image forming apparatus, and explanatory diagram of a state in which a small size recording material is set on the tray out of specification Determination flow chart for small size throughput down control and one-sided throughput down control Flow chart for small size throughput down control Flow chart for control of downshift throughput Diagram showing the relationship between the length of the recording material in the conveyance direction when the recording material is passed through the nip with the central conveyance reference and the temperature arrival time of the sub-thermistor The figure showing an example of the relationship between the conveyance direction length of a recording material, and judgment threshold temperature The figure showing an example of the relationship between the conveyance direction length of a recording material, and judgment threshold time

Explanation of symbols

18: heater, 65: main thermistor, 66: sub-thermistor,
21: DC controller, 48: recording material sensor, 49: top sensor,
68: Misalignment sensor, Ta: Determination threshold temperature, ta: Determination threshold time

Claims (5)

An image forming apparatus for forming an image on a recording material, comprising an elongated heating body that heats a recording material that generates heat when energized and carries the image, and a recording material that is narrower than a heating region width in the longitudinal direction of the heating body Detection by the first temperature detection means for detecting the temperature of the area through which the recording material passes, the second temperature detection means for detecting the temperature of the area through which the recording material does not pass with respect to the width of the heat generation area, and detection by the first temperature detection means Control means for controlling energization to the heating body so as to maintain the temperature at a set temperature, and for performing control to reduce the number of recording material outputs per unit time based on the temperature detected by the second temperature detection means; In an image forming apparatus having
A length detection means for detecting the length of the recording material in the transport direction;
Recording material presence / absence detecting means for detecting the presence / absence of the recording material on the side opposite to the second temperature detecting means with respect to a recording material conveyance reference for conveying the recording material to the heating body;
Have
The control means is a threshold temperature for performing control to reduce the number of output recording materials per unit time based on the detected temperature of the second temperature detecting means for the recording materials having different lengths in the conveyance direction of the recording material. And the threshold temperature is less when the recording material is not detected by the recording material presence / absence detection means and the length of the recording material detected by the length detection means is longer than a reference length. An image forming apparatus that is set to be higher. An image forming apparatus for forming an image on a recording material, comprising an elongated heating body that heats a recording material that generates heat when energized and carries the image, and a recording material that is narrower than a heating region width in the longitudinal direction of the heating body First temperature detecting means for detecting the temperature of the area through which the recording material passes, second temperature detecting means for detecting the temperature of the area where the recording material narrower than the width of the heat generating area does not pass, and the first temperature detection Control for controlling energization to the heating body so as to maintain the detected temperature of the means at a set temperature, and performing control for reducing the number of recording material outputs per unit time based on the detected temperature of the second temperature detecting means And an image forming apparatus comprising:
A length detection means for detecting a length in the conveyance direction of the recording material conveyed to the heating body;
Recording material presence / absence detecting means for detecting the presence / absence of the recording material on the side opposite to the second temperature detecting means with respect to a recording material conveyance reference for conveying the recording material to the heating body;
Have
The control means is a threshold time for performing control to reduce the number of output recording materials per unit time based on the detected temperature of the second temperature detecting means for the recording materials having different lengths in the conveyance direction of the recording material. And the threshold time is shorter when the recording material is not detected by the recording material presence / absence detection means and the length of the recording material detected by the length detection means is longer than a reference length. An image forming apparatus that is set to be shorter.   The image forming apparatus according to claim 2, wherein the threshold time is a time required for the temperature detected by the second temperature detection unit to reach a certain threshold temperature.   The image forming apparatus according to claim 1, wherein the control unit changes the conveyance timing of the recording material as control for reducing the number of recording material outputs per unit time.   The image forming apparatus according to claim 1, wherein the control unit changes a process speed for forming an image on the recording material as control for reducing the number of recording material outputs per unit time.